Added a frequently asked question to README

Author: felipebueno

README.markdown

@@ -82,6 +82,10 @@ __Q. How can I open a NERDTree automatically when vim starts up if no files were
 
 A. Stick this in your vimrc `autocmd vimenter * if !argc() | NERDTree | endif`
 
+__Q. How can I map a specific key or shortcut to open NERDTree?__
+
+A. Stick this in your vimrc to open NERDTree with `Ctrl+n` (you can set whatever key you want): `map <C-n> :NERDTreeToggle<CR>`
+
 __Q. How can I close vim if the only window left open is a NERDTree?__
 
 A. Stick this in your vimrc: